1. Field of Invention
The present invention relates to a microbiological process for the production of polymers, to novel polymers produced through such a process, and to microorganisms for use in such a process.
2. Description of Related Art
It is known that many bacteria are able to accumulate polymers, such as polymers of 3-hydroxybutyric acid (PHB), within their cells as an energy reserve material. For instance in EP-B-15669, PHB is produced through the aerobic culturing of certain strains of Methylobacterium organophilum on a substrate comprising methanol.
PHB is a straight chain polymer formed essentially from monomer repeat units having four carbon atoms having the structure EQU --O.CH(CH.sub.3).CH.sub.2.CO--
The term polymer hereinafter implies, unless stated otherwise, a straight chain polymer.
The monomer repeat unit from which PHB is formed is an example of a so-called C4 monomer.
Polymers have also been microbiologically produced, wherein at least some of the monomer repeat units have more than four carbon atoms. Thus in EP-A-69497, a process is disclosed wherein a polymer is formed comprising monomer repeat units of PHB in association with monomer repeat units having greater than four carbon atoms. The process involves cultivating a suitable microorganism, such as Alcaligenes eutrophus NCIB 11599, on a substrate comprising an organic acid that can be metabolised by the microorganism to the appropriate monomer repeat unit. (The abbreviations NCIB and NCIMB herein refer to the National Collections of Industrial and Marine Bacteria Ltd., PO Box 31, 135 Abbey Road, Aberdeen AB9 8DG, United Kingdom). For example, where the substrate is propionic acid, containing three carbon atoms, the microorganism synthesises monomer repeat unit of the form EQU --O.CH(C.sub.2 H.sub.5).CH.sub.2.CO--
the monomer repeat unit of the polymer of 3-hydroxyvaleric acid, having five carbon atoms, a so-called C5 monomer. Effectively, the microorganism can increase the number of carbon atoms present in the monomer repeat unit by two, over the number of carbon atoms present in the organic acid of the substrate.
De Smet et al, Journal of Bacteriology, May 1983, pp 870 to 878, have shown that poly-B-hydroxyoctanoate, a polymer formed essentially from monomer repeat units having eight carbon atoms, i.e. C8 monomers, is produced and accumulated by Pseudomonas oleovorans ATCC 29347, when the microorganism is cultivated on n-octane, i.e. a straight chain alkane. (The abbreviation ATCC herein refers to the American Type Culture Collection, 12301 Park Lawn Drive, Rockville, Md., 20852 USA).
Brandl et al, Applied and Environmental Microbiology, August 1988, pp 1977 to 1982, have further shown that polymers comprising monomer repeat units having up to eleven carbon atoms, i.e. C11 monomers, can be produced microbiologically. The microbiological process disclosed by Brandl et al involves the cultivation of Pseudomonas oleovorans ATCC 29347 on substrates comprising one of a number of different assimilable straight chain carbon compounds, such as alkanoic acids, alkanes and alkenes. It is shown that no polymer is produced unless an assimilable straight chain carbon compound having at least six carbon atoms is used in the substrate, and that the maximum yield of polymer occurs when an assimilable straight carbon compound having eight or nine carbon atoms is used.
Brandl et al also show that a trend exists such that the number of carbon atoms present in the monomer repeat units corresponds to the number of carbon atoms in the assimilable straight chain carbon compound used. Various monomer repeat units are shown to be produced which differ from one another by the number of carbon atoms contained therein. The number of carbon atoms present in some of the monomer repeat units are shown to differ by one to two from the number of carbon atoms present in the assimilable straight chain carbon compound. Where the assimilable straight chain carbon compound has fewer than ten carbon atoms the most common, i.e. modal, number of carbon atoms to be found in the monomer repeat unit is the same as the number of carbon atoms in the assimilable straight chain carbon compound. However, where the assimilable straight chain carbon compound contains ten carbon atoms this trend is not continued and less than 12 mol % of the monomer units have ten carbon atoms.
Thus, where the monomer repeat units are required to contain more than four carbon atoms the substrate on which the microorganism is grown comprises assimilable straight chain carbon compounds having within two carbon atoms of the required number, and particularly the same number of carbon atoms. Thus where a monomer repeat unit contains ten carbon atoms, i.e. CIO monomer, the substrate has to contain at least one assimilable straight chain carbon compound containing eight carbon atoms.
Lageveen et al, Applied and Environmental Microbiology, December 1988, pp 2924 to 2932 also employed Pseudomonas oleovorans ATCC 29347 to produce a range of polymers comprising monomer repeat units having up to twelve carbon atoms. Lageveen et al cultivated the microorganism on a substrate containing an alkane or alkene having between six to twelve carbon atoms. It is stated by Lageveen et al that the number of carbon atoms in the monomer repeat units having the largest number of carbon atoms always corresponded to the number of carbon atoms contained in the alkane or alkene used in the substrate. It is also disclosed that when the substrate contained an alkane having six carbon atoms, only a small amount of polymer was produced, the polymer consisting of monomer units having six carbon atoms. Furthermore, when the substrate contained an alkene having six carbon atoms no polymer was produced.
In a survey of the accumulation of novel polymers by bacteria, Haywood et al, Biotechnology Letters, 1989, Vol. 11, No. 7, pages 471 to 476 essentially confirmed the work of Lageveen et al.
Those assimilable straight chain carbon compounds, used by Brandl et al, and Lageveen et al, can in themselves be difficult, and expensive to produce. Therefore, the microbiologically produced polymers that have been synthesised from such assimilable straight chain carbon compounds also tend to be expensive.
Further, the conversion efficiency of existing microbiological processes for the production of such polymers is also low, thereby adding to the cost of the finished polymer.